I have the same problem. Additionally, L4D no longer connects to multiplayer. Single Player works fine, but when I try to connect to an online game, the connection crashes everytime, although my steam connection is fine and wifi works fine.

Same here. The addons that I had left clicked on before this update show up in game but all my others ones such as skins and the like are unaccessible now. I can't choose between skins for weapons and items anymore, whether to run a campaign or not; nothing. Apparently there is supposed to be an "Addons" selection in the menu? My friend can see hers plain as day and mine is missing. Heck, I haven't even been on since the update and now this? Fix.

mine alittle diffrent. when installed the game everything work fine add on an everything but when i turn the computer off or restart. it act like i never downloaded anything from the workshop. or sub anyone. any clue on what it my be? (the only way i can fix this is i reinstall the game.. an i dont feel like doing that.. at all.)

Thanks to some dialogue on a L4D2 video on Youtube, I found out that Rayman's Mutation mod actually disabled the add-ons section for me so I unchecked it. Whether or not that issue has been addressed in a fix of his, I don't know.

I was just recently struggling with the same problem but I've now fixed it. At first I tried moving around the files from the workshop folder to the addons folder but that did not work. I also reinstalled the game completely (!) and verified files etc. What did work however was deleting a file in the left 4 dead 2/left4dead2 folder called "addonlist.txt". I looked in it before deleting it and noticed it had a few "old" addons I used before the workshop existed. After deleting the file and starting the game all the addons popped up fine in the list!

I had a similar problem a few months ago, all the L4D2 Workshop files just stopped working and the game crashed. What I did was I deleted everything from the workshop, and downloaded them regularly from http://www.gamemaps.com/l4d2/ then everything worked fine.